1. Technical Field
This invention generally relates to the stabilization of halogen-containing polymers such as polyvinyl chloride (PVC) resins. In particular, this invention relates to overbased metal carbonate/carboxylate liquid microemulsion compositions capable of providing static and dynamic thermal stability to food grade PVC resins subjected to thermal degradation.
2. Description of the Related Art
In general, PVC resins can be stabilized by a range of stabilizers. Typically, compounds containing heavy metals such as, for example, lead, cadmium and barium, have been utilized for this purpose but are problematic from an environmental and toxilogical standpoint, particularly in case of food grade PVC resins where the presence of most heavy metal-containing material is especially prohibited. Thus, there continues to be a need for effective stabilizers and stabilizer compositions in PVC resins that are substantially free of lead and other heavy metals which pose environmental and toxilogical problems.
The use of solid calcium and zinc carboxylates for stabilizing polymers, particularly food grade (xe2x80x9cFDA compliantxe2x80x9d) PVC resins, is known. Attempts to provide such stabilizers in a liquid form to facilitate their handling and incorporation into the resins has been a technologically challenging goal.
Accordingly, there remains a need for liquid PVC stabilizers that have a long shelf life and impart thermal stability and satisfactory processability when incorporated in PVC resins. Additionally, it would also be desirable to provide liquid PVC stabilizers which reduce the tendency of the stabilized PVC resin compositions to form xe2x80x9cfogxe2x80x9d upon moderate heating.
It is an object of the present invention to provide stable, effective liquid microemulsion stabilizer compositions for the thermal stabilization, i.e., static and dynamic thermal stabilization, of halogen-containing polymers.
It is a particular object of this invention to provide food grade compositions of halogen-containing polymers such as PVC containing FDA compliant liquid microemulsions as thermal stabilizers.
In keeping with these and other objects of the invention, there is provided a liquid microemulsion composition imparting static and dynamic thermal stability to halogen-containing polymers which comprises:
a) a metal carbonate/carboxylate obtained from the reaction of an oxide and/or hydroxide of a metal selected from the group consisting of sodium, potassium, calcium, magnesium, zinc and mixtures thereof and an aliphatic acid in which the aliphatic moiety contains up to about 30 carbon atoms and carbon dioxide in an oil;
b) one or more non-phenolic compounds having about two or about three hydroxyl groups; and,
c) one or more polyols and/or alcohol ethoxylates and/or alcohol propoxylates having from about 6 to about 24 carbon atoms in the alcohol, and 0 to 3 ethylene oxide units and/or 0 to 3 propylene oxide units.
Another aspect of the present invention is a halogen-containing polymer composition having improved resistance to deterioration mediated by heat, i.e., improved thermal stability, in addition to improved static and dynamic thermal stability comprising a halogen-containing polymer and a stabilizing amount of the foregoing liquid microemulsion composition effective to impart static and dynamic thermal stability to the halogen-containing polymer composition.